1. Field of the Invention
The present invention relates to a cell voltage detecting system for a fuel cell and a drive voltage maintaining method for a voltage detector.
2. Description of the Related Art
A cell voltage detecting system for detecting cell voltages in a battery cell stack including a plurality of cells such as fuel cells is known.
Fuel cells are generally used in a form of a fuel stack including a plurality of cells connected in series, each cell generating an emf through an electrochemical reaction between a fuel gas mainly containing hydrogen and an oxidizing gas. Such fuel cells are installed, for example, in a fuel cell vehicle.
Cell voltages tend to vary depending on a fuel gas density, a temperature, and a temperature distribution in the fuel cell stack. For example, the cell voltages of the fuel cell are zero volts when the fuel gas is not supplied to the fuel cell. Further, decrease in cell voltages of a part of cells in the fuel cell stack may influence the whole of the fuel stack in a life and a stability of the fuel stack. Accordingly, it is required to monitor (detect) a status of each cell voltage in the fuel cell stack.
JP 2007-232417 A discloses at paragraph 0006 a cell voltage detecting system using an A/D converter as a voltage detector for detecting a cell voltage. The cell voltage detecting system disclosed in JP 2007-232417 A uses the fuel cell itself as a power supply for driving the voltage detector. However, as mentioned above, the voltage of the fuel cell may largely vary. Thus, with variation of the voltage of the fuel cells a voltage detection error may occur. In the cell voltage detecting system disclosed in JP 2007-232417 A, a monitoring circuit for monitoring a voltage for driving the voltage detector and an external power supply for driving the monitoring circuit are additionally provided.